St Andrews' wife is a Roman Catholic. According to the Act of Settlement 1701, no person who is Catholic or marries a Catholic could succeed to the throne of any country whose constitution subscribes to that Act. Therefore, from his marriage until 26 March 2015, St Andrews was barred from succession to the throne. After the Succession to the Crown Act 2013 came into effect on 26 March 2015, he is no longer barred from succession and is currently 38th in line (the most senior to be restored to the succession list), although his two older children, as Catholics, are still barred.

The Dukedom of Kent is not subject to the Act of Settlement or the Succession to the Crown Act 2013, so St Andrews' son and heir, Lord Downpatrick, is in line to become the first Roman Catholic duke or earl of Kent since the Reformation.